<div class="panel panel-primary">
  <div class="panel-heading">NgFor的用法</div>
  <div class="panel-body">
    <div [ngSwitch] = "mapStatus">
      <p *ngSwitchCase = "'下载中'">下载中.....</p>
      <p *ngSwitchCase = "'正在读取'">正在读取.....</p>
      <p *ngSwitchDefault>系统繁忙</p>
    </div>
  </div>
</div>